The eye and seeing

Almost all living things are sensitive to light. You know for example that the clam closes its shell when a shadow falls on it. This action is made possible by a number of special cells that line the edge of the shell. Light falling on these cells that excites them. Messages or nerve impulses then pass to the muscles that close the shell, and say that a simple reflex nervous completed.    watch videosBut this light sensitivity is very different from the vision. A clam can not be said of view, in the sense that man can see. Before you can actually see an animal has to have two things. First, there must be real eyes eyes, not just a shell. Second, the eyes must be connected to a well-developed brain. There are many animals eyes perfectly, is as good as ours, in fact, but see very little. The explanation for this surprising fact is that these animals have well developed eyes in relation to the brain that are still primitive. They can use their eyes and brain to respond to simple light reflex. But they can not really, because there are no centers in the brain controls vision.

For example, a fish may seem to prefer one type of bait to another. However, it is unlikely to actually see one of them. And certainly, you can make a conscious choice between them. This is simply because the fish were not vision centers. The eyes of all higher animals are fundamentally similar. Each eye is composed of a series of structures contained within a body of substantially spherical eyeball. Most of the eyeball is enclosed in a bone cavity in the front of the head, only a small part is visible from outside. The eye is partially hidden and surrounded by a variety of other structures, the eyelids, tear glands and ducts, muscles, blood vessels and nerves, to name just a few. Each has a special role to play in the eye body work efficiently.

The eye is most often compared to a chamber. In fact, the two are very similar. In both cases, a sensitive screen on which the light rays are focused. Both have a goal to focus. Both have a dark lining to avoid reflection and blurring. And finally the eyes and the camera can be adjusted to give sharp images at different distances. In the case of eye focus adjustment of objects at various distances is known as accommodation.